Stabilizer for trimethylphosphate



United States Patent 3,275,717 STABELIZIER FOR TRIMETHYLPHOSPHATE HarryS. Butler, Baton Rouge, La., assignor to Ethyl Corporation, New York,N.Y., a corporation of Virginia No Drawing. Filed Apr. 29, 1963, Ser.No. 276,183 6 Claims. (Cl. 260-963) This invention relates to thestabilization of automotive ignition control compound mixes and inparticular is directed to those mixes containing trimethylphosphate,either in its pure form or in concentrated solution with otheradditives.

Trimethylphosphate as commercially supplied today normally contains avery small trace of water. However, this minute trace of waterhydrolyzes the trimethylphosphate over a period of time to produce thecorresponding orthophosphoric acids. This acid produces a cloudiness orwhite precipitate in the trimethylphosphate when it is allowed to standin contact with steel. While this white precipitate in no mannersubstracts from the ability of the remaining t-rimethylphosphate tofunction as an ignition control agent, it does present a materialhandling problem in that if it is allowed to build up appreciably, itmight clog screens or other handling equipment, besides beingobjectionable from an aesthetic viewpoint. Moreover, it corrodes suchequipment which in itself is objectionable. Thus, a method of inhibitingtrimethylphosphate containing minute quantities of corrosive acidswithout impairing its effectiveness as an ignition control agent wouldrepresent a desirable contribution to the art.

An object of this invention is to stabilize trimethylphosphate ascommercially supplied and when in contact with a ferrous material. Amore specific object is to stabilize trimethylphosphate containingminute traces of acids by adding thereto a compound which does notimpair its effectiveness as an ignition control agent.

These objectives are accomplished pursuant to this invention by addingan amine compound to trimethylphosphate, or a highly concentratedsolution thereof, containing slight traces of water and/or acids. Themost suitable amines a-re the lower alkyl amines, that is, thosecontaining from 1 through 6 carbon atoms per alkyl group. Especiallypreferred are the tertiary alkyl amines wherein the alkyl groups aresimilar (and most preferably, the same) since these compounds are morereadily available. Of these, the tributyl amines are especiallypreferred since they have a boiling point close to that oftrimethylphosphate. Thus, a preferred embodiment of this invention istrimethylphosphate and concentrated mixtures thereof containing an aminehaving a boiling point close to that of the trimethylphosphate. Whileamines having a boiling point lower than that of trimethylphosphate areperfectly suitable for use pursuant to the practice of this invention,they naturally have more tendency to vaporize out of solution and hencebe lost for their intended use. On the other hand, amines having aboiling point higher than that of trimethylphosphate, while usually moreeffective, are generally less soluble and hence present a mixingproblem. Moreover, their increased cost also makes them less attractive.While tertiary amines are preferred, secondary and primary amines underthe right conditions can be employed pursuant to the practice of thisinven- "ice tion. However, they are generally less stable and henceoffer no technical advantage over the preferred tertiary amines.

Exemplary of the compounds that can be employed as stabilizers pursuantto this invention are: trimethylamine, triethylamine, tri-n-propylamine,triisopropylamine, tri-nbutylamine, tri-sec-butylamine,tri-tert-butylamine, triisobutylamine, tri-n-amylamine,tri-n-hexylamine, t-rin-octylamine, tri-n-decylamine, ethyldibutylamine, and the like.

Surprisingly, the concentration of the amine to achieve these desirableend results is generally less than that quantity necessary to completelyneutralize any contained acids in the trimethylphosphate. Withoutwishing to be bound by theory, it is thought that the amine coats theferrous material in contact wit-h the trimethylphosphate andconsequently, theoretical neutralization of the objectionable phosphoricacid is not required. Generally speaking, it has been found that aconcentration as low as 0.2 weight percent amine based on the totalsolution up to about 2.0 weight percent, usually not above 1.0 weightpercent, is suitable to adequately inhibit [both neattrimethylphosp-hate and highly concentrated solutions as commerciallyavailable today. By highly concentrated solutions is meant solutions inwhich trimethylphosphate is present at about 50 percent by weight in asuitable solvent, such as hydrocarbon solvents or in other antiknockfluid compositions.

-It is to be understood of course that concentrations greater than 2.0weight percent based on the weight of trimethylphosphate can beemployed. However, concentrations less than this value are preferredsince generally speaking such amounts, besides achieving the objectivesof this invention, are readily soluble in trimethylphosphate at ambienttemperature conditions. The extent of contact between thetrimethylphosphate and a ferrous material primarily influences thenecessary amount of amine that must be present in order to stabilize thetrimethylphosphate. The only time the concentration of acids in thetrimethylphosphate appears to influence such determination is where thetrimethylphosphate is stored for unduly long periods of time, say on theorder of six months. Even so, for the latter situation seldom is morethan 2.0 weight percent required.

\Another distinct advantage of the instant invention is that noinsoluble products are formed by the addition of the amine to thetrimethylphosphate. This is highly unexpected in light of the fact thatone might expect that the amine, being a base, when added to thetrimethylphosphate containing acids would result in the formation ofsalt like materials which would precipitate out of solution and thuscompound the problem solved by this invention rather than rectify it.For example, employing a cornmeroially available source of neattrimethylphosphate con taining 0.26 weight percent water and 0.016 meq./g. acid, the addition of 0.5 weight percent of the preferredtri-nbutylamine is highly effective in preventing the formation of anyprecipitate when the trimethylphosphate is allowed to stand in contactwith ferrous material or in a steel container. When the resultantsolution is added to a fuel, either as such or first blended withantiknock fluid compounds, test results confirm the fact that thetrimethylphosphate is identically effective to that of trimethylphos- CBphate which has not been stabilized as taught by way of this invention.

The following examples wherein all parts are by weight unless otherwisespecified demonstrate the effectiveness of an amine for stabilizingtrimethylphosphate.

The following tests were conducted with neat trimethylphosphate to whichwas added approximately 4 times the specification level of mixed acidsnormally present in commercial grade trimethylphosphate. The testmixture was analyzed and found to contain 0.28 weight percent water and0.137 meq./ g. acid. The neat trimethylphosphate was then tested atseveral temperature levels.

The first temperature level was at room temperature which wasapproximately 70 to 75 F. About 50 milliliters of the neattrimethylphosphate solution containing the excess acid was added to eachof numerous containers wherein a mild steel specimen was placed. Thecontainers were then capped to prevent contact with the atmosphere. Theywere then observed at least twice a week for cloudiness or the formationof a white precipitate.

The second temperature level investigated was at about 110 F. About 25milliliters of the neat trimethylphosphate containing the excess acidwas added to numerous test tubes each containing a mild steel specimen.The test tubes were then closed to the atmosphere and placed in aconstant temperature bath controlled at 110 F. The solutions were thenobserved at least twice a week for the formation of a white precipitateor cloudiness.

The results of these test runs are tabulated below.

TABLE I Acid Temp. Inhibitor Test N0. Present (F.) Added, Wgt.Observations qJ Percent Cloudy (3 days). Cloudy (17 days). Clear (137days). Clear (137 days). Cloudy (17 days). Clear (64 days). Clear (73days). Clear (137 days). Clear (94 days). Clear (94 days).

Cloudy days).

Clear (137 days). Clear (137 days). Cloudy (1 day). Cloudy (2 days).Cloudy (92 days). Clear (136 days). Cloudy (2 days). Clear (63 days).

Clear (73 days).

Clear (136 days). Clear (94 days). Clear (94 days). Cloudy (2 days).Clear (136 days) Clear (136 days).

*Tri-n-amylamine. TrLn-butylarnine. ***Triethylamine.

A next series of tests were run wherein the trimethylphosphate containeda similar amount of excess acid as in the above runs except that thetrimethylphosphate was dissolved in about a 50 weight percenthydrocarbon solvent. The results are given in Table II.

TABLE II Acid Temp. Inhibitor Test No. Present (F.) Added, Wgt.Observations (meq./g.) Percent Cloudy (1 day). Clear (94 days). Clear(94 days). Cloudy (1 day). Clear (94 days). Clear (94 days). Cloudy (1day). Clear (94 days). Clear (94 days).

. 1.0 BuzN 2.0mm Clear (94 days):

The above tests clearly demonstrate the effectiveness of an amine as astabilizer for trimethylphosphate containing traces of water and/or acidwhen in contact with a ferrous material.

When employing trimethylphosphate containing a concentration of amine astaught herein as an ignition control agent, no reduction in itseffectiveness as such is indicated.

I claim:

1. A mixture comprising trimethylphosphate present in the form of atleast a concentrated solution thereof and further comprising minutequantities of water sufficient to form phosphoric acids, containing anamount of a tertiary alkyl amine less than the theoretical amount whichwould be necessary to neutralize said acids.

2. A mixture comprising trimethylphosphate present in the form of atleast a concentrated solution thereof and further comprising a trace ofwater or acid stabilized by the addition of a tertiary alkyl aminewherein each alkyl group contains from 1 to 6 carbon atoms, said aminebeing present in less than the theoretical amount which would benecessary to neutralize said acids.

3. Stabilization of a mixture comprising trimethylphosphate present inthe form of at least a concentrated solution thereof by the additionthereto of a tertiary alkyl amine having a boiling point of about 379F., said amine being present in less than the theoretical amount whichwould be necessary to neutralize any acids present.

4. Stabilization of a mixture comprising trimethylphosphate present inthe form of at least a concentrated solution thereof by the addition oftri-n-butylamine thereto, said amine being present in less than thetheoretical amount which would be necessary to neutralize any acidspresent.

5. Stabilized neat trimethylphosphate containing 0.2 to 1.0 weightpercent tri-n-butylamine, said amine being present in less than thetheoretical amount which would be necessary to neutralize any acidspresent.

6. Stabilized neat trimethylphosphate containing 0.5 weight percenttri-n-butylamine, said amine being present in less than the theoreticalamount which would be necessary to neutralize any acids present.

References Cited by the Examiner UNITED STATES PATENTS 2,114,866 4/1938Vaughn 260461.316

CHARLES B. PARKER, Primary Examiner.

FRANK M. SIKORA, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 5 275,717 September 27 1966 Harry S. Butler It is hereby certified that errorappears in the above numbered patent requiring correction and that thesaid Letters Patent should read as corrected below.

Column 4, line 33, for "or acid stabilized" read or phosphoric acids ormixtures thereof stabilized Signed and sealed this 26th day of September1967.

(SEAL) Attest:

ERNEST W. SWIDER Attesting Officer EDWARD J. BRENNER Commissioner ofPatents

1. A MIXTURE COMPRISING TRIMETHYLPHOSPHATE PRESENT IN THE FORM OF ATLEAST A CONCENTRATED SOLUTION THEREOF AND FURTHER COMPRISING MINUTEQUANTITIES OF WATER SUFFICIENT TO FORM PHOSPHORIC ACIDS, CONTAINING ANAMOUNT OF A TERTIARY ALKYL AMINE LESS THAN THE THEORETICAL AMOUNT WHICHWOULD BE NECESSARY TO NEUTRALIZE SAID ACIDS.
 5. STABILIZED NEATTRIMETHYLPHOSPHATE CONTAINING 0.2 TO 1.0 WEIGHT PERCENTTRI-N-BUTYLMAINE, SAID AMINE BEING PRESENT IN LESS THAN THE THEORETICALAMOUNT WHICH WOULD BE NECESSARY TO NEUTRALIZE ANY ACIDS PRESENT.